1. Field of the Invention
This invention relates to a fiber-optic temperature-measuring apparatus which is based on the photo-luminescence of a solid material, which is subjected to the temperature to be measured.
For many applications of temperature measurement, it is of great interest to be able to use a non-electrical method, which utilizes light transmission in optical fibers. Such applications are especially advantageous in explosive environments or in areas with strong electric or magnetic fields.
2. Description of the Prior Art
A disadvantage associated with certain known measuring apparatus of this kind is that they cannot be positioned at any place without special measures. A further drawback is that it is not possible to distinguish changes in transmitted radiation which are due to the temperature, from other radiation changes that may occur for other reasons. In practice, known fiber-optic temperature-measuring apparatus has to be calibrated with a known temperature after the apparatus has been positioned at the place of measurement, and this involves a complication.
One solution to the above-mentioned problems, and other associated problems, is disclosed in published European patent application No. 0006530 in which the temperature-dependent, spectral absorption capacity is measured in a material which is exposed to the temperature to be measured, optical fibers then being used for passing light to said material and for passing out part of this light after absorption in the material. The measuring apparatus is provided with means for determining the absorption capacity at at least two wavelength ranges of the light falling into the material.
Another measuring apparatus, which may be used for fiber-optic temperature measurement, is the object of Brogaardh et al's U.S. patent application Ser. No. 152,746 (related to the instant application by a common assignee). In this application, an optical fiber is arranged in optical contact with a thyristor and a light signal emitted from the thyristor is used, among other things, as a measure of the temperature of the thyristor.
It is also known to use in temperature measurements, a material which emits radiation of wavelength that is dependent on the temperature of the material.
The present invention is an improvement of this known technique which is a solution to the above-mentioned problems. Furthermore, there is no requirement for an electric current to pass through the solid material. It is a parallel solution to the above-mentioned measuring apparatus, which used the spectral absorption capacity of a material.